A medical X-ray apparatus has an X-ray generator for projecting X-ray and an X-ray detector for receiving the X-ray from the X-ray generator, receives the X-ray generated at the X-ray generator and transmitted through an object to be examined, thereby obtaining an X-ray transmitted image based on the transmitted X-ray amount. In case of panoramic radiography, X-ray is projected while the X-ray generator and the X-ray detector are moved around the object along a predetermined orbit and a two-dimensional panoramic X-ray image of a curved sectional plane is obtained.
The applicant of this invention has proposed a digital panoramic radiography apparatus in which the X-ray detector is a two-dimensional X-ray detector and a panoramic X-ray image on an optional sectional plane is produced from a plurality of frame images successively obtained from the two-dimensional X-ray detector (refer to patent citations 1 and 2). A sectional plane which has an equal distance from the detection surface of the X-ray detector which moves along a predetermined orbit is called as a “tubular sectional plane”.
According to the digital panoramic radiography apparatus in the patent citations 1 and 2, a panoramic X-ray image is produced by combining a plurality of frame images obtained by panoramic radiography. In this case, a panoramic X-ray image on an optional sectional plane is produced by setting the fetch interval and the shift amount of the frame images which are used for calculation for producing a panoramic X-ray image. Specifically in the digital panoramic radiography apparatus in the patent citation 1, a panoramic X-ray image produced with the image information on the tubular sectional plane which is different from each area can be produced by changing the fetch interval and the shift amount of the frame images which are used for calculation for producing a panoramic X-ray image.
According to the digital, panoramic radiography apparatus in the patent citations 1 and 2, respectively, when a panoramic X-ray image is produced by adding the image data of a plurality of frame images, a panoramic X-ray image on an objective sectional plane can be produced when the fetch interval and the shift amount are set at an appropriate value. Specifically in the digital panoramic radiography apparatus in the patent citation 1, the facial direction of the sectional plane can be made optional when the image data on the tubular sectional plane which are selected to each area is combined on a sheet of panoramic X-ray image. In addition, according to a medical X-ray apparatus which executes panoramic radiography with a frame image like this digital panoramic radiography apparatus, the image data per the tubular sectional plane can be extracted from a plurality of frame images obtained by panoramic radiography with respect to an optional local region.
According to the panoramic imaging apparatus of the patent citation 3, the frame data obtained by panoramic radiography are synthesized to produce a panoramic X-ray image and a shutter for shielding X-ray is provided on the front surface of an X-ray tube to execute panoramic radiography only on a part of a dental arch. However, the patent citation 3 only discloses a structure for projecting X-ray on an object to be examined in a fixed distance during panoramic radiography on the entire dental arch. Namely, the patent citation 3 discloses that the X-ray radiation area is partially restricted along the scanning direction of X-ray beam.
The panoramic radiography apparatus in which electronic image data are obtained in a two-dimensional X-ray detector and a panoramic X-ray image is produced by an image process has been already proposed. In such a panoramic radiography apparatus like those in the patent citations 1 to 3, a plurality of frame images being X-ray transmitted images of a dental arch are rendered to shift operation to produce a panoramic X-ray image. Such production of panoramic X-ray image by the shift operation of the frame images has an advantage that a clear panoramic X-ray image is produced by synthesizing a sectional plane with plural planes in which a sectional plane on a desired position can be set.
The panoramic radiography apparatus in the patent citations 1 and 2 only proposes an idea that so called a panoramic sectional plane traverses longitudinally all over the dental arch and shift operation of frame image is executed based on the panoramic sectional plane of the entire dental arch. In addition, the panoramic radiography apparatus in the patent citation 2 discloses restriction of X-ray beam in a scanning direction, however, it does not disclose or suggest restriction of X-ray beam in a direction intersecting a scanning direction.